1. Field of the Invention
The present invention generally relates to a mobile communication terminal, and more particularly to a Planar Inverted-F Antenna (PIFA).
2. Description of the Related Art
The current miniaturization trend in mobile communication terminals is being accelerated. According to this miniaturization trend, mobile communication terminals are now being produced with internal antennas that produce smaller overall mobile terminals.
A typical internal antenna is a Planar Inverted-F Antenna (PIFA). FIG. 1 illustrates an exemplary structure of a conventional PIFA. Referring to FIG. 1, the PIFA is provided with a ground plane 102, a patch 100, a feeding pin 104, and a shorting pin 106. Here, the shorting pin 106 can be replaced with a shorting plate. When an electric current is fed to the patch 100 mounted above the finite ground plane 102 through the feeding pin 104, the patch 100 and the ground plane 102 are excited and act as a radiating device. A frequency bandwidth, gain, and resonant frequency of the PIFA depend upon the height, width, and depth of the patch 100 and a distance z between the feeding pin 104 and the shorting pin 106 or the shorting plate.
One advantage of the PIFA is that it can be embedded within a mobile communication terminal. However, there is a drawback in that the PIFA is limited by a space within the mobile communication terminal. In case of the PIFA as described above, antenna frequency characteristics such as a frequency bandwidth, gain, resonant frequency, and so on can vary according to the height, width, and depth of the patch 100 and other factors. Because the PIFA is limited by the space within the mobile communication terminal, the antenna frequency characteristics are also limited by the space within the mobile communication terminal. The mobile communication terminal in which the PIFA is embedded is designed to maximize the frequency characteristics of the PIFA for one specific frequency band.
Currently, various frequency bands are used in regions of the world. For example, in South Korea, cellular and personal communication service (PCS) systems use frequency bands of 800 MHz and 1700 MHz, respectively. In the United States, the cellular and PCS systems use frequency bands of 800 MHz and 1900 MHz, respectively. In China, a frequency band of 2100 MHz is used. In Romania and Russia, the cellular system uses a frequency band of 450 MHz. In Poland and the Ukraine, a frequency band of 850 MHz is used. Accordingly, the PIFA is designed to operate over various frequency bands, so that a user can receive a mobile communication service even when moving to another country.
Structural features of the mobile communication terminal significantly influence the frequency characteristics of the PIFA. For example, the frequency characteristics of an antenna change over different frequency bands and according to a slide or folder structure or an open or close state thereof. Here, the open state is a state in which a folder is open in the folder structure, while the close state is a state in which the folder is closed in the folder structure. The open and close states also exist in the slide-type mobile communication terminal. When the PIFA is designed, elements such as the patch 100, the ground plane 102, the shorting pin 106, and the feeding pin 104 capable of influencing the frequency characteristics are designed such that the antenna frequency characteristics can be optimized for specific structural features and can be minimized for other structural features.
When the user uses the mobile communication terminal in a different frequency band, the influence to the frequency characteristics for the specific structural features can vary with the different frequency band in use. For example, the effect on the frequency characteristics in the open state of the folder may be different between 800-MHz and 450-MHz bands. Accordingly, there is a problem in that the conventional PIFA cannot satisfy multi-frequency characteristics according to the structural features of a specific mobile communication terminal.